1. Field of the Invention
The present invention relates generally to electrical supply plug and, more particularly, to an electrical supply plug that is designed to promote safety by preventing electrical power to be supplied to an appliance unless the appliance is properly connected and the appliance is turned on. A main benefit of the present invention is that it is childproof.
2. Description of the Prior Art
It is well known to provide mains electrical supply safety sockets wherein the live and neutral outlets are covered with an insulating plate which is adapted to retract when the ground pin of a three pin plug is inserted into the ground outlet of the socket. It is generally arranged in such systems for the ground pin to be slightly longer than both the neutral and live pins in order to facilitate the operation of the safety mechanism.
The major drawback with such a system is that the insulating plate is liable to jam. If it jams in the closed position the socket is unusable but the safety device is inoperative. Furthermore, such a system is not childproof in that any object having a shape resembling a ground pin may be inserted into the ground outlet of the socket, thereby retracting the insulating plate and overriding the safety mechanism. Indeed, this approach is sometimes adopted in order to connect the supply leads from an electrical appliance directly to a mains electrical supply without first attaching a plug to the appliance, which is obviously highly unsatisfactory from a safety point of view.
Other inventive efforts have been made to promote safety with respect to mains electrical supply sockets. For example, U.S. Pat. No. 4,623,209 discloses such a safety promoting electrical socket. A brief description of this prior art device is now given.
U.S. Pat. No. 4,623,209 (Mangone) discloses an electrical safety socket including normally open switches for connecting live and neutral feeders to their respective socket outlets. The switches close when substantially parallel live and neutral pins of an electric plug are inserted into their corresponding socket outlets simultaneously. In such an arrangement, the insertion of each plug pin is adapted to pull 2 respective levers located external to the plug housing and articulated to a corresponding one of the switches. Such an arrangement allows independent operation of the switches and, since the levers are accessible from outside the plug housing, they may easily be operated independently of a plug being inserted into the socket. Consequently, foreign objects may be introduced into either socket outlet and the corresponding switch may be manually closed so as to complete the connection. Although both of the above-mentioned prior art techniques provide some degree of safety with respect to preventing an accidental or an otherwise unintentional connection to a mains electrical supply, neither prevent such a connection from occurring by anything other than a simple mechanical arrangement, which are often unreliable. Thus, it would be preferable that a similar technique be provided with at least the same degree of safety as the above-mentioned prior art techniques, but also increased reliability. Such a similar technique would be desirable since it is frequently becoming a requirement to include electrical safety features in the construction of new homes, office buildings, and the like. It is therefore desirable to provide such a similar technique and to overcome the shortcomings of the above-mentioned prior art techniques in this area.